What happens if Trump invades Greenland? (In 2 minutes)

By Yusra Suedi (PhD, Assistant Professor of International Law at University of Manchester)

1. Who does Greenland belong to?

Denmark.

Greenland is self-governing, meaning it runs its own internal affairs (like education, health, and natural resources), but it is not a sovereign state.

Denmark retains control over defense, currency, and foreign policy, and is internationally recognized as the sovereign state.

2. But Trump said “The fact [Denmark] had a boat land there 500 years ago does not mean they own the land.” Is that true?

Partly, but misleading.

It’s true that discovery (i.e. a boat landing there) alone has never been sufficient to establish sovereignty under international law.

But that’s not how Denmark got Greenland.

Denmark ran the place for a long time (making laws, administering it, policing it, managing trade, and handling its foreign affairs).

The Permanent Court of International Justice (PCIJ) confirmed its ownership in 1933, and the U.S. had already accepted it in 1916.

3. Can Trump legally buy Greenland?

Yes, but only if both Denmark and the Greenlanders agree.

Denmark must agree:

Under international law, territory can be transferred by cession: a treaty between countries that often involves payment (like a sale agreement).

In this case, it would require an agreement between the U.S. and Denmark.

The U.S. has done this before: Louisiana (1803), Alaska (1867), and the Danish West Indies (1917).

Greenlanders must agree:

Under international law, people have a right to self-determination, meaning they get to decide their own future.

The International Court of Justice (succeeding the PCIJ) has confirmed this: in 2019 it decided the UK couldn’t take the Chagos Islands from Mauritius without the people’s consent.

Greenlanders have already said they don’t want to join the U.S., so any sale without their approval would likely be illegal.

4. Can Trump force Denmark to sell Greenland?

No.

Any treaty signed under coercion is invalid under international law.

5. Can Trump pay the Greenlanders to agree?

No.

The Greenlanders’ right to self-determination must be exercised freely, without coercion or inducement.

Paying people to change their political will would violate this right.

6. Can Trump invade Greenland?

No.

Use of force is prohibited, except in self-defense or with UN Security Council approval. Neither applies here.

7. What if he tried anyway?

That would be illegal annexation: a type of use of force involving taking another country’s land.

Modern international law forbids it.

8. What would NATO do?

Both Denmark and the U.S. are NATO members, but NATO was never designed for one member to attack another. It lacks enforcement mechanisms against member aggression and can’t kick a member out.

NATO could call consultations under Article 4 and declare the U.S. action a treaty violation, but unified military action would be impossible.

But Denmark has the right to self-defense under the UN Charter, and other countries could support Denmark with troops, aid, or sanctions, even if NATO as a whole doesn’t act.

European states would likely reorganise their own defense arrangements, and the U.S. would face massive political and legal isolation.

No country could legally recognise the U.S.’s illegal annexation of Greenland.

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